Liquid crystal display device

ABSTRACT

A liquid crystal display device comprising a TFT substrate having pixels each including a common electrode formed on an organic passivation film, an interlayer insulating film formed so as to cover the common electrode, a pixel electrode having a slit and formed on the interlayer insulating film, a through-hole formed in the organic passivation film and the interlayer insulating film, and a source electrode electrically conducted to the pixel electrode via the through-hole. A taper angle at a depth of D/2 of the through-hole is equal to or more than 50 degrees. The pixel electrode covers part of a side wall of the through-hole but does not cover the remaining part of the side wall of the through-hole. This configuration facilitates the alignment film material to flow into the through-hole, thereby solving a thickness unevenness of the alignment film in vicinity of the through-hole.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2013-254205 filed on Dec. 9, 2013, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a display device. The invention moreparticularly relates to a liquid crystal display device in whichreduction in transmissivity is small even in a case where the screen isa high-definition screen, the liquid crystal display device having fewpixel defects in the high-definition screen.

2. Description of the Related Art

In a liquid crystal display device, a thin film transistor (TFT)substrate in which pixels each including a pixel electrode, a TFT, andthe like are formed like a matrix, a counter substrate facing the TFTsubstrate and having color filters formed at positions in facingrelation to the pixel electrodes on the TFT substrate are arranged, andliquid crystal is sandwiched between the TFT substrate and the countersubstrate. The liquid crystal display device forms images by controllinglight transmissivity of liquid crystal molecules at each pixel.

The liquid crystal display device is flat and lightweight. Thus, theapplication of the liquid crystal display device has been extended invarious fields. A small liquid crystal display device has widely beenused in portable information terminals, such as mobile phones,smartphones, and Digital Still Cameras (DSCs). A viewing anglecharacteristic is a key issue in liquid crystal display devices. Theviewing angle characteristic relates to a phenomenon that brightness orchromaticity changes between cases where a screen of the liquid crystaldisplay device is viewed from front and where the screen is viewed froman oblique direction. An In-Plane Switching (IPS, which is a registeredtrademark of Japan Display Inc.) system causing a horizontal electricfield to operate liquid crystal molecules has an excellent viewing anglecharacteristic.

Although various IPS systems exist, e.g., a system in which a commonelectrode is formed in a planar and solid manner and in which acomb-teeth pixel electrode is arranged above the common electrode so asto sandwich an insulating film between the pixel electrode and thecommon electrode, and to cause an electric field generated between thecommon electrode and the pixel electrode to rotate liquid crystalmolecules. This system can increase the transmissivity. Accordingly,this system is currently a mainstream. The common electrode and aninterlayer insulating film are formed on an organic passivation filmserving also as a planarizing film.

Meanwhile, if a pixel size is reduced by providing the liquid crystaldisplay device with a high-definition screen, a ratio of a radialcross-sectional area of a through-hole connecting between a pixelelectrode and a source electrode of the TFT is increased.

In the above IPS liquid crystal display device, if the ratio of theradial cross-sectional area of the through-hole to the pixel sizeincreases, an adhesion strength between the organic passivation film andthe interlayer insulating film formed thereon decreases. Thus, a problemoccurs, in which the interlayer insulating film peels off.JP-2011-59314-A describes a device which reduces stress on theinterlayer insulating film and which prevents peeling-off of theinterlayer insulating film by forming the interlayer insulating film notin the through-hole but only on the organic passivation film.

If a diameter of the through-hole is reduced as the pixel size isreduced by provision of the high-definition screen, a taper angle of awall portion of the through-hole (hereinafter sometimes referred to alsoas a taper angle of the through-hole) should be increased. On the otherhand, an alignment film is used to initially align the liquid crystal. Amaterial of the alignment film, which is initially in a liquid state, isapplied by flexographic printing, inkjet printing, or the like.

If the taper angle of the through-hole is increased, applying thematerial of the alignment film may cause a phenomenon that the materialof the alignment film does not go into the through-hole. Then, a displaydefect, such as a luminance unevenness, occurs due to a fact that noalignment film exists in the through-hole, or to a thickness unevennessof the alignment film in a periphery of the through-hole.JP-2007-322563-A describes a device that varies a height at a peripheryof the through-hole thereby to facilitate the alignment film to flowinto the through-hole.

If the pixel size is reduced, a ratio of a pixel electrode to each pixelis relatively reduced, so that a transmissivity at each pixel isdecreased. According to photoalignment of the alignment film initiallyaligning the liquid crystal, an alignment treatment can be performed onan inner wall portion of the through-hole. Thus, the inner wall portionof the through-hole can be used as a display area. JP-2013-140386-Adescribes a device that increases the transmissivity at each pixel byutilizing photoalignment to utilize an inside of the through-hole as adisplay area.

SUMMARY OF THE INVENTION

Recently, even a small liquid crystal display device requires ahigh-definition screen such as a Video Graphics Array (VGA) screen using640×480 dots. Incidentally, a dot is a set of three pixels, i.e., a redpixel, a green pixel, and a blue pixel. Therefore, the VGA screen usespixels the number of which is 1920×480. To enable VGA on a 3-inchscreen, the shorter diameter of each pixel is set to be very small,e.g., 32 μm. Further, another high-definition screen has been developed,in which the shorter diameter of each pixel is less than 30 μm.

Even if each pixel is reduced in size, in order to maintain apredetermined transmissivity, it is necessary to arrange the TFT, thethrough-hole, and the like in a small area, and to increase the ratio ofthe area of the pixel electrode to the pixel as much as possible. If theradial cross-sectional area of the through-hole is reduced, the taperangle of the through-hole is increased. Thus the material of thealignment film becomes difficult to flow into the through-hole.Consequently, a display defect, such as a luminance unevenness, occurs.

If a height difference is provided among upper surrounding portions ofthe through-hole like the device described in JP-2007-322563-A, what iscalled an organic passivation film cannot be used. This is because ofthe following reasons. That is, the organic passivation film is formedthick to have a thickness of 2 μm to 4 μm. Thus, a surface of theorganic passivation film is flat. Consequently, it is difficult to forma height difference among the surrounding portions of the through-hole.

On the other hand, to meet demands for uniformizing a thickness of theliquid crystal layer, some types of the liquid crystal display devicesneed to use an organic passivation film. Since the organic passivationfilm is formed thick to have a thickness of 2 μm to 4 μm, a problem ofincreasing the radial cross-sectional area of the through-hole becomesincreasingly serious if a through-hole is formed in the organicpassivation film.

FIG. 14 is a perspective view illustrating the above problem of an IPSliquid crystal display device. FIG. 15 is a cross-sectional view takenalong line I-I shown in FIG. 14. In FIG. 14, a pixel electrode 107having a slit 1071 provided therein is connected through a through-holeto a source electrode 102. An interlayer insulating film (not shown)exists under the pixel electrode 107. Under the interlayer insulatingfilm, a common electrode (not shown) exists.

FIG. 15 is a cross-sectional view illustrating a through-hole 109 and aneighborhood thereof. In FIG. 15, a gate insulating film 101 is formedon a TFT substrate 100. On the gate insulating film 101, a sourceelectrode 102 extending from a TFT is formed. An inorganic passivationfilm 103 is formed on the source electrode 102 and the gate insulatingfilm 101. An organic passivation film 104 is formed on the inorganicpassivation film 103. A common electrode 105 is formed on the organicpassivation film 104. An interlayer insulating film 106 is formed so asto cover the common electrode 105. A pixel electrode 107 having a slitis formed on the interlayer insulating film 106. This structure may beconfigured without providing an inorganic passivation film under theorganic passivation film.

In FIG. 15, a counter substrate 200 is arranged opposite to the TFTsubstrate 100. A liquid crystal layer 300 is sandwiched between the TFTsubstrate 100 and the counter substrate 200. A black matrix 202 isformed on part of the counter substrate 200 in facing relation to thethrough-hole 100. A color filter 201 is formed on part of the countersubstrate 200 in facing relation to the pixel electrode 107. An overcoatfilm 203 is formed so as to cover the black matrix 202 and the colorfilter 201. An alignment film 108 is formed on the overcoat film 203.

At the side of the TFT substrate 100, the pixel electrode 107 isconnected to the source electrode 102 via the through-hole 109 formed inthe inorganic passivation film 103, the organic passivation film 104,and the interlayer insulating film 106. If the screen is changed to ahigh-definition screen so as to reduce the area of each pixel, in orderto ensure a transmissivity at each pixel, it is necessary to increasethe taper angle of the inner wall of the through-hole 109 and to reducethe radial cross-sectional area of the through-hole 109.

However, as illustrated in FIG. 15, if the taper angle of thethrough-hole 109 is large, the alignment film material 108, which isinitially liquid, is difficult to flow into the through-hole 109 from atop face 1091 (see FIG. 17) of the through-hole 109. Thus, a problemoccurs, in which no alignment film is formed in the through-hole. Inaddition, another problem occurs, in which the thickness of thealignment film 108 is increased on the periphery of the through-hole109, so that the thickness unevenness of the alignment film 108 occurs.Then, display defects, such as a luminance unevenness, occur due toabsence of an alignment film in the through-hole 109, or due to thethickness unevenness of the alignment film in the periphery of thethrough-hole 109.

The reason why thus the alignment film does not flow into thethrough-hole 109 is considered as follows. FIGS. 16A and 16B illustratea contact angle of the alignment film material 108. FIG. 16A illustratesa case where the alignment film material 108 is dropped onto the planarpixel electrode 107 formed of ITO. In this case, the contact angle is θ.FIG. 16B illustrates a contact angle in a case where the alignment filmmaterial 108 of a liquid form exists and is near the top face 1091 ofthe through-hole 109 having a taper angle α.

In FIG. 16B, the contact angle in vicinity of the top face of thethrough-hole 109 is β which is larger than θ. That is, it can be saidthat the alignment film material 108 is more difficult to wet and spreadat the top face of the through-hole 109 than on the pixel which is flat.Here, assuming that “α” denotes the taper angle of the through-hole 109,that “β” denotes the contact angle of the alignment film material 108 atthe top face of the through-hole 109, and that “θ” denotes the contactangle of the alignment film material 108 on the planar pixel electrode107 shown in FIG. 16A, a relationship among α, β, and θ is given by thefollowing expression.

θ≦β≦α+θ

Accordingly, the alignment film material 108 spreads over the pixelelectrode 107 formed of ITO in vicinity of the through-hole 109 withoutgoing into the through-hole 109. That is, as illustrated in FIG. 15, thealignment film material 108 is formed thick on the periphery of thethrough-hole 109.

An object of the present invention is to provide a liquid crystaldisplay device using an organic passivation film in a TFT substrate,which is configured to facilitate each alignment film material to gointo a through-hole even in a case where the area of each pixel isreduced using a high-definition screen, and where the radialcross-sectional area of the through-hole is limited.

The present invention is accomplished to overcome the above problems.Specific means according to the present invention are as follows.

(1) A liquid crystal display device includes: a TFT substrate havingpixels each having a common electrode formed on an organic passivationfilm, an interlayer insulating film formed so as to cover the commonelectrode, a pixel electrode having a slit and formed on the interlayerinsulating film, a through-hole formed in the organic passivation filmand the interlayer insulating film, and a source electrode electricallyconducted to the pixel electrode via the through-hole; a countersubstrate having color filters formed in facing relation to the pixels,and a black matrix formed among the color filters; and liquid crystalsandwiched between the TFT substrate and the counter substrate. When thethrough-hole formed in the organic passivation film assumes across-section in which a top face is defined on the side of the countersubstrate and a bottom face is defined on the side of the sourceelectrode, the top face has a diameter larger than that of the bottomface, and the through-hole has a depth of D, then, a taper angle at adepth of D/2 of the through-hole is equal to or more than 50 degrees.The common electrode covers part of a side wall of the through-hole butdoes not cover the remaining part of the side wall of the through-hole.

(2) A liquid crystal display device includes: a TFT substrate havingpixels each having a common electrode formed on an organic passivationfilm, an interlayer insulating film formed so as to cover the commonelectrode, a pixel electrode having a slit and formed on the interlayerinsulating film, a through-hole formed in the organic passivation filmand the interlayer insulating film, and a source electrode electricallyconducted to the pixel electrode via the through-hole; a countersubstrate having color filters formed in facing relation to the pixels,and a black matrix formed among the color filters; and liquid crystalsandwiched between the TFT substrate and the counter substrate. When thethrough-hole formed in the organic passivation film assumes across-section in which a top face is defined on the side of the countersubstrate and a bottom face is defined on the side of the sourceelectrode, the top face has a diameter larger than that of the bottomface, and the through-hole has a depth of D, then, a taper angle at adepth of D/2 of the through-hole is equal to or more than 50 degrees,and the slit of the pixel electrode extends to a depth of 1 μm or morefrom a top surface of the organic passivation film or to a depth of D/4or more from the top surface of the organic passivation film.

According to the present invention, a liquid crystal display deviceusing a high-definition screen to thereby reduce the area of each pixeland also using an organic passivation film in a TFT substrate isprovided, which can stably form an alignment film in a through-hole,even if a through-hole diameter is reduced. Accordingly, the liquidcrystal display device according to the present invention can prevent adisplay defect such as a luminance unevenness due to absence of thealignment film or due to the thickness unevenness of the alignment filmin the periphery of the through-hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a pixel of a liquid crystal display device towhich the present invention is applied;

FIG. 2 is a perspective view illustrating a pixel electrode and athrough-hole according to a first embodiment;

FIG. 3 is a cross-sectional view taken on line A-A shown in FIG. 2;

FIG. 4 illustrates a definition of a taper angle of the through-hole;

FIG. 5 illustrates an example of a planar shape of the through-hole;

FIG. 6 is a perspective view illustrating a pixel electrode and athrough-hole according to a second embodiment;

FIG. 7 is a cross-sectional view taken on line E-E shown in FIG. 6;

FIG. 8 is a perspective view illustrating a pixel electrode and athrough-hole of another configuration of the second embodiment;

FIG. 9 is a cross-sectional view taken on line F-F shown in FIG. 8;

FIG. 10 is a perspective view illustrating a common electrode and athrough-hole according to a third embodiment;

FIG. 11 is a cross-sectional view taken on line G-G shown in FIG. 10;

FIG. 12 is a perspective view illustrating a common electrode and athrough-hole according to a fourth embodiment;

FIG. 13 is a cross-sectional view taken on line H-H shown in FIG. 12;

FIG. 14 is a perspective view illustrating a pixel electrode and athrough-hole according to the related art;

FIG. 15 is a cross-sectional view taken on line I-I shown in FIG. 14;

FIGS. 16A and 16B illustrate a definition of a contact angle; and

FIG. 17 is a perspective view illustrating a moving direction of amaterial of an alignment film according to the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is described in detail with referenceto embodiments.

First Embodiment

FIG. 1 is a plan view of a pixel in a TFT substrate of a liquid crystaldisplay device to which the present invention is applied. FIG. 1illustrates an example of an IPS liquid crystal display device. In FIG.1, scanning lines 10 extend in a lateral direction and are arranged in alongitudinal direction at a predetermined pitch PY. Video signal lines20 extend in the longitudinal direction and are arranged in the lateraldirection at a predetermined pitch PX. Each region surrounded by thescanning line 10 and the video signal line 20 is a pixel.

In FIG. 1, a gate electrode 11 branches from the scanning line 10. Asemiconductor layer 30 is formed on the gate electrode 11. On the otherhand, a source electrode 102 is formed on the semiconductor layer 30.The source electrode 102 extends in the direction of a pixel electrode107 and increases in width at part thereof overlapping with a pixelelectrode 106 and under a through-hole 109. The source electrode 102serves also, as a light shielding film preventing occurrence of lightleakage in the through-hole 109.

In FIG. 1, the pixel electrode 107 having a slit 1071 is formed like arectangle. An interlayer insulating film is formed under the pixelelectrode 107. A planar common electrode is formed under the interlayerinsulating film. Lines of electric force from the pixel electrode 107are formed so as to pass through a slit 1071 toward the commonelectrode.

In FIG. 1, the pixel electrode 107 is connected to the source electrode102 via the through-hole 109. The through-hole 109 is formed in anorganic passivation film whose thickness is large. Thus, thethrough-hole 109 has a taper so as to have a larger-diameter top face1091 and a smaller-diameter bottom face 1092. According to the presentembodiment, the source electrode 102 is formed so as to be slightlylarger than the through-hole 109, and serves also as a light shieldingfilm for the through-hole 109. The source electrode 102 may be shapedcross-sectionally like a circle corresponding to a shape of thethrough-hole 109. To obtain a desired transmissivity, the pixel may beconfigured so that part of the top face 1091 or the bottom face 1092 ofthe through-hole 109 protrudes from the source electrode 102.

FIG. 2 is a perspective view illustrating a relationship between thepixel electrode 107 and the through-hole 109. In FIG. 2, the pixelelectrode 107 having the slit 1071 covers the through-hole 109 and iselectrically conducted to the source electrode 102. However, accordingto the present embodiment, the pixel electrode 107 does not cover theentire inner wall of the through-hole 109. In an outside of the pixelelectrode 107, the pixel electrode 107 does not cover the inner wall andthe periphery of the top face of the through-hole 109.

In a configuration illustrated in FIG. 2, when an alignment filmmaterial 108 of a liquid form is applied, the alignment film material108 spreads over a SiN film configuring the interlayer insulating film106 from an ITO film configuring the pixel electrode 107. Thus, thealignment film material 108 flows into the through-hole 109, startingfrom a boundary portion of a step-like part, which is about 50 nm, ofthe ITO film. Further, since the alignment film material 108 is easierto wet and spread on the SiN film than on the ITO film, the alignmentfilm material 108 can flow into the through-hole 109 via the interlayerinsulating film 106 made of SiN.

Accordingly, as illustrated in FIG. 3, the alignment film material 108flows into the through-hole 109. Even in a periphery of the through-hole109, the alignment film 108 can be formed so as to have a uniformthickness. FIG. 3 is a cross-sectional view of the liquid crystaldisplay device, which corresponds to a cross-section taken along lineA-A shown in FIG. 2. Description of configurations of each of the TFTsubstrate 100 and the counter substrate 200 illustrated in FIG. 3, whichhave been described with reference to FIG. 15, is omitted here.

A main difference between the configurations illustrated in FIGS. 3 and15 is that the pixel electrode 107 in the configuration illustrated inFIG. 3 is not completely formed on the entire through-hole 109. Thepixel electrode 107 is formed on a left-side periphery and a left-sideinner wall of the through-hole 109, as viewed in FIG. 3. However, thepixel electrode 107 is not formed on a right-side periphery and aright-side inner wall of the through-hole 109, as viewed in FIG. 3. Thatis, the alignment film material 108 illustrated in FIG. 3 flows into thethrough-hole 109 from the right side of the through-hole 109, as viewedin FIG. 3. With this configuration, even if a taper angle of thethrough-hole 109 is large, the alignment film material 108 can stablyflow into the through-hole 109.

Incidentally, if the taper angle of the through-hole 109 is about 50degrees in the conventional configuration, at a certain frequency, aphenomenon occurs, in which the alignment film material 108 does notflow into the through-hole 109. Further, if the taper angle of thethrough-hole 109 is equal to or more than 60 degrees, the alignment filmmaterial 108 hardly flows into the through-hole 109. Accordingly, adisplay unevenness occurs over a wide range of the screen.

Meanwhile, as illustrated in FIG. 3, because an organic passivation film104 serves as a planarizing film, the organic passivation film 104 isformed thick, e.g., a thickness of 2 μm to 4 μm. That is, the organicpassivation film 104 is very thick, as compared with other films.Therefore, it can be considered that the shape of the through-hole 109is determined by the shape of the through-hole formed in the organicpassivation film 104. That is, the taper angle of the inner wall of theorganic passivation 109 can be considered as the taper angle of thethrough-hole formed in the organic passivation film 104.

FIG. 4 is a cross-sectional view for defining the taper angle of thethrough-hole 109. The through-hole 109 in this case is the through-hole109 formed in the organic passivation film 104. As illustrated in FIG.4, assuming that a depth of the through-hole 109 formed in the organicpassivation film 104 is D, a taper angle α of the through-hole 109 isdefined as an angle formed by a tangent line to the wall at a depth ofD/2, i.e., half the depth of the through-hole 109, and a line connectingbetween cross-sections of top surfaces of the organic passivation film104.

A cross-section of the through-hole 109 varies depending on a planarshape of the through-hole 109 or at what part of the through-hole 109 iscut to form the cross-section. FIGS. 5A to 5C illustrate definitions ofa cross-section in various cases of the planar shape of the through-hole109. FIG. 5A corresponds to a case where the planar shape of thethrough-hole 109 is a circle. In this case, a cross-section taken alongline B-B passing through the center of the circle corresponds to FIG. 4.FIG. 5B corresponds to a case where the planar shape of the through-hole109 is a square. In this case, a cross-section taken along line C-C onan axis of the square corresponds to FIG. 4. FIG. 5C corresponds to acase where the planar shape of the top face of the through-hole 109 is arectangle. In this case, a cross-section taken along line D-D on a shortaxis of the through-hole 109 corresponds to FIG. 4. That is, in a casewhere a plan view of the top face of the through-hole 109 has a longaxis and a short axis, the taper angle of the through-hole 109 isdefined by the taper angle α on a short-axis cross-section, which isillustrated in FIG. 4.

In a conventional structure, if the angle α illustrated in FIG. 4 isabout 50 degrees, at a certain frequency, the phenomenon occurs, inwhich the alignment film material 108 does not flow into thethrough-hole 109. If the angle α is equal to or larger than 60 degrees,the phenomenon occurs, in which the alignment film material 108 hardlyflows into the through-hole 109. However, according to the presentembodiment, even in a case where the angle α is equal to or larger than50 degrees, the alignment film material 108 can flow into thethrough-holes 109 formed in all pixels. In addition, according to thepresent embodiment, even in a case where the angle α is equal to orlarger than 60 degrees, the alignment film material 108 can flow intothe through-holes 109 formed in all pixels. Accordingly, according tothe present embodiment, display defects due to a thickness failure ofthe alignment film can be resolved.

Second Embodiment

FIG. 6 is a perspective view illustrating a relationship between a pixelelectrode 107 and a through-hole 109 according to a second embodiment ofthe present invention. In FIG. 6, a slit 1071 formed in a pixelelectrode 10 extends in a through-hole 109. In the slit 1071, a surfacethereof is formed of SiN configuring an interlayer insulating film 106,instead of ITO. Thus, an alignment film material 108 of a liquid formcan flow into the through-hole 109, starting from a boundary portion ofa step-like part of the ITO film. Further, because the surface is formedof the SiN film in the slit 1071, the alignment film material 108 iseasier to wet and spread in this case than a case of using the ITO film.Thus, also from this aspect, the alignment film material 108 is easierto flow into the through-hole 109.

FIG. 7 is a cross-sectional view of a liquid crystal display device,which corresponds to a cross-section taken on line E-E shown in FIG. 6.FIG. 7 is similar to FIG. 3 illustrating the first embodiment, exceptfor a configuration of the pixel electrode 107. In FIG. 7, the pixelelectrode 107 extends in the through-hole 109 from the right side of thethrough-hole 109, and is connected to a source electrode 102. On theother hand, at the left side of the through-hole 107 shown in FIG. 7,the slit 1071 is formed, so that the pixel electrode 107 does not exist.Surfaces of an inner wall of the through-hole 109 and a periphery of atop face thereof are formed of SiN configuring the interlayer insultingfilm 106. Accordingly, the alignment film material 108 flows into thethrough-hole 109 from the left side of the through-hole 109, whichcorresponds to the slit 1071.

FIG. 8 illustrates another configuration of the present embodiment. InFIG. 8, the slit 1071 of the pixel electrode 107 is not formed to abottom face of the through-hole 109. FIG. 9 is a cross-sectional view ofthe liquid crystal display device, which corresponds to a cross-sectiontaken on line F-F shown in FIG. 8. FIG. 9 is similar to FIG. 7, exceptfor a configuration of the pixel electrode 107.

In FIG. 8, in a left-side vicinity of a top face of the through-hole109, and a portion extending from the top face to a position at a depthX thereof, the slit 1071 is formed, and no ITO film configuring thepixel electrode 107 exists. In FIG. 8, assuming that a depth of thethrough-hole 109 is D, part in which no ITO exists extends from the topface of the through-hole 109 to the position at the depth of X thereof.Under this part, an ITO film configuring the pixel electrode 107 exists.

Incidentally, a value of X is equal to or larger than a smaller one ofD/4 and 1 μm. That is, if a portion where the SiN film configuring theinterlayer insulating film 106 is exposed is smaller than X shown inFIG. 9, effects of causing the alignment film material 108 to flow intothe through-hole 109 are small. Incidentally, the depth D of thethrough-hole 109 shown in FIG. 9 corresponds to a range from a topsurface of the interlayer insulating film 106 to a top surface of thepixel electrode 107 provided in the through-hole 109. The depth X isdetermined with reference to a top surface of the interlayer insulatingfilm 106. Since the thickness of the insulating film and the ITO film issmall in comparison with the thickness of the organic passivation film,similar effects can be obtained even if the depth of D of thethrough-hole 109 shown in FIG. 9 is changed to the depth of D of thethrough-hole 109 formed in the organic passivation film 104 shown inFIG. 4, and if the value of X is changed to represent a value from thetop surface of the organic passivation film 104.

Thus, even according to the present embodiment, the alignment filmmaterial 108 can preferably flow into the through-hole 109. According tothe present embodiment, even in a case where the angle α is equal to orlarger than 50 degrees, the alignment film material 108 can flow intothe through-holes 109 respectively formed in all pixels. In addition,according to the present embodiment, even in a case where the angle α isequal to or larger than 60 degrees, the alignment film material 108 canflow into the through-holes 109 formed in all pixels. Accordingly,display defects due to a thickness failure of the alignment film 108 canbe resolved by the present embodiment.

Third Embodiment

A third embodiment is an IPS liquid crystal display device configured sothat a pixel electrode 107 formed in a planar and solid manner isarranged on a lower side, and that a common electrode 105 having a slit1051 is provided on an upper side via an interlayer insulating film 106,contrary to the first embodiment.

FIG. 10 is a perspective view illustrating a relationship between acommon electrode 105 and a through-hole 109 according to the thirdembodiment. In FIG. 10, the common electrode 105 having the slit 1051does not cover the entire inner wall of the through-hole 109. In anoutside of the common electrode 105, the common electrode 105 does notcover the inner wall and the periphery of the top face of thethrough-hole 109.

FIG. 11 is a cross-sectional view of the liquid crystal display device,which corresponds to the cross-section taken on line G-G shown in FIG.10. The common electrode 105 is formed on a left-side periphery and aleft-side inner wall of the through-hole 109, as viewed in FIG. 11.However, the common electrode 105 is not formed on a right-sideperiphery and a right-side inner wall of the through-hole 109.

When an alignment film material 108 of a liquid form is applied in sucha configuration, the alignment film material 108 spreads over a SiN filmconfiguring the interlayer insulating film 106 from an ITO filmconfiguring the common electrode 105, similarly to the first embodimentin which surface condition is approximately same to that of the thirdembodiment. As illustrated in FIG. 11, the alignment film material 108flows into the through-hole 109, so that the thickness of the alignmentfilm 108 can be uniformized even in a periphery of the through-hole 109.

According to the present embodiment, even when the angle α is equal toor larger than 50 degrees, the alignment film material 108 can flow intothe through-holes 109 formed in all pixels. In addition, according tothe present embodiment, even when the angle α is equal to or larger than60 degrees, the alignment film material 108 can stably flow into thethrough-holes 109 formed in all pixels. Accordingly, display defects dueto a thickness failure of the alignment film can be resolved by thepresent embodiment.

Fourth Embodiment

A fourth embodiment is an IPS liquid crystal display device configuredso that a pixel electrode 107 formed in a planar and solid manner isarranged on a lower side, and that a common electrode 105 having a slit1051 is provided on an upper side via an interlayer insulating film 106,contrary to the second embodiment.

FIG. 12 is a perspective view illustrating a relationship between acommon electrode 105 and a through-hole 109 according to the fourthembodiment. In FIG. 12, a slit 1051 formed in the common electrode 105extends in the through-hole 109. In an inner wall part of the slit 1051,a surface thereof is formed of SiN configuring an interlayer insulatingfilm 106, instead of ITO, similarly to the second embodiment.Accordingly, via the slit 1051 formed in the common electrode 105, thealignment film material 108 of a liquid form can flow into thethrough-hole 109, starting from a boundary portion of a step-like partof the ITO film.

FIG. 13 is a cross-sectional view of the liquid crystal display device,which corresponds to a cross-section taken on line H-H shown in FIG. 12.FIG. 13 is similar to FIG. 11 illustrating the third embodiment, exceptfor a configuration of the common electrode 105. Since the slit 1051 isprovided at the left side of the through-hole 109, as viewed in FIG. 13,the common electrode 105 does not exist there. Surfaces of an inner walland a periphery of a top face of the through-hole 109 are formed of SiNconfiguring the interlayer insulating film 106. Thus, the alignment filmmaterial 108 easily flows into the through-hole 109 from the left sideof the through-hole 109, which corresponds to the slit 1051.

In a case where the slit 1051 of an uppermost layer is not formed to abottom face of the through-hole 109, as shown in FIG. 8 illustrating thesecond embodiment, similarly, assuming that the depth of thethrough-hole 109 is D, a slit is formed in a left-side vicinity of a topface of the through-hole 109, and a portion extending from the top faceto a position at a depth X thereof. Under this slit, an ITO filmconfiguring the pixel electrode 107 exists.

Incidentally, a value of X is equal to or larger than a smaller one ofD/4 and 1 μm. For example, in a case where the slit 1051 reaches abottom face of the through-hole 109, the value of X is equal to thevalue of D. According to the present embodiment, even in a case wherethe taper angle α is equal to or larger than 50 degrees, the alignmentfilm material 108 can flow into the through-holes 109 formed in allpixels. Accordingly, according to the present embodiment, a displayunevenness due to a thickness failure of the alignment film 108 can beresolved.

Incidentally, although it has been described that each of the pixelelectrode and the common electrode is formed of an ITO film, the ITOfilm may be changed to a transparent electrically-conductive film, suchas an IZO film. Further, in the second to fourth embodiments, the slitformed in the pixel electrode or in the common electrode extends in thethrough-hole. Thus, the liquid crystal can be driven in thethrough-hole. Therefore, the liquid crystal display device may have astructure in which the entire slit or part of the slit is exposed fromthe source electrode.

Incidentally, the present invention can be applied to an alignment filmsubjected to a photo-alignment treatment using polarized ultravioletrays as well as the alignment film subjected to the alignment treatmentusing a rubbing method.

In the foregoing description, it has been described that the colorfilters are formed in the counter substrate. However, according to thepresent invention, the color filters may be formed in the TFT substrate.In this case, a color filter may be used instead of the organicpassivation film. Alternatively, both of the organic passivation filmand the color filter may be used.

In the foregoing description, a term “black matrix” is used. It is notedthat “black matrix” includes the meaning of so called “black stripes” orits equivalent structures.

What is claimed is:
 1. A liquid crystal display device comprising: atransistor substrate including; a thin film transistor having a sourceelectrode, an organic insulating film formed on the thin film transistorand having a through hole which has a side wall, a common electrodeformed on the organic insulating film, an interlayer insulating filmformed on the common electrode, and a pixel electrode formed on theinterlayer insulating film and electrically connected to the sourceelectrode via the through-hole, a counter substrate having a lightshielding film, and a liquid crystal layer sandwiched between thetransistor substrate and the counter substrate, wherein the pixelelectrode covers the side wall of the through-hole, and wherein thepixel electrode has a slit including a first end, and the first end isoverlapped with the side wall.
 2. The liquid crystal display deviceaccording to claim 1, wherein the pixel electrode has a slit.
 3. Theliquid crystal display device according to claim 2, wherein the slitoverlaps with a part of the side wall.
 4. The liquid crystal displaydevice according to claim 1, wherein the through-hole formed in theorganic insulating film, the through-hole has a cross-section in which atop face is defined on the side of the counter substrate and a bottomface is defined on the side of the source electrode, the top face havinga diameter larger than that of the bottom face, the through-hole havinga depth of D, a taper angle at a depth of D/2 of the through-hole isequal to or more than 50 degrees.
 5. The liquid crystal display deviceaccording to claim 4, wherein the slit of the pixel electrode extends toa depth of 1 μm or more from a top surface of the organic insulatingfilm or to a depth of D/4 or more from the top surface of the organicinsulating film.
 6. The liquid crystal display device according to claim1, wherein the taper angle of the through-hole is equal to or more than60 degrees.
 7. The liquid crystal display device according to claim 1,wherein an alignment film is formed in the through-hole.
 8. The liquidcrystal display device according to claim 1, wherein the interlayerinsulating film is formed by silicon nitride.
 9. A liquid crystaldisplay device comprising: a transistor substrate including; a gateline, a thin film transistor, having a source electrode, connected tothe gate line, an organic insulating film formed on the thin filmtransistor and having a through hole which has a side wall, a commonelectrode formed on the organic insulating film, an interlayerinsulating film formed on the common electrode, and a pixel electrodeformed on the interlayer insulating film and electrically connected tothe source electrode via the through-hole, a counter substrate having alight shielding film, and a liquid crystal layer sandwiched between thetransistor substrate and the counter substrate, wherein the pixelelectrode covers the side wall of the through-hole, and wherein thepixel electrode has a first end disposed between an edge of the throughhole and the gate line, in a plan view, and the first end is overlappedwith the side wall.
 10. The liquid crystal display device according toclaim 9, further comprising an alignment film contacts with the pixelelectrode, wherein the common electrode has a slit.
 11. The liquidcrystal display device according to claim 9, wherein the slit overlapswith a part of the side wall.
 12. The liquid crystal display deviceaccording to claim 9, wherein the through-hole formed in the organicinsulating film, the through-hole has a cross-section in which a topface is defined on the side of the counter substrate and a bottom faceis defined on the side of the source electrode, the top face having adiameter larger than that of the bottom face, the through-hole having adepth of D, a taper angle at a depth of D/2 of the through-hole is equalto or more than 50 degrees.
 13. The liquid crystal display deviceaccording to claim 12, the slit of the common electrode extends to adepth of 1 μm or more from a top surface of the organic insulating filmor to a depth of D/4 or more from the top surface of the organicinsulating film.
 14. The liquid crystal display device according toclaim 9, wherein the taper angle of the through-hole is equal to or morethan 60 degrees.
 15. The liquid crystal display device according toclaim 9, wherein an alignment film is formed in the through-hole. 16.The liquid crystal display device according to claim 9, wherein theinterlayer insulating film is formed by silicon nitride.